Coronary sinus lead for pacing the left atrium

ABSTRACT

A pacing lead for implantation in a coronary sinus having an opening and a wall defining an interior and presenting a diameter dimension. The pacing lead includes an elongated lead body, a resilient fixation element, and at least one electrode on either the lead body or the fixation element. The fixation element extends from the pacing portion and defines a loop structure laterally adjacent the pacing portion. The loop structure presents a predetermined width dimension greater than the diameter dimension of the coronary sinus, wherein when the loop structure is inserted into the opening of the coronary sinus, the loop structure is laterally compressed by the wall of the coronary sinus and the electrode is biased against the wall of the coronary sinus.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/144,447, entitled CORONARY SINUS LEAD FOR PACING THE LEFTATRIUM, filed Jun. 3, 2005, hereby fully incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to pacing leads. Moreparticularly, the present invention relates to pacing leads for stablepacing of the left atrium through the coronary sinus.

BACKGROUND OF THE INVENTION

Pacing to the left atrium is important for successful bi-atrial pacing.The pacing to the left atrium is usually accomplished by placing apacing lead into the coronary sinus, which is a venous structureaccessible through the right atrium of the heart and serves to drain thecoronary veins. The coronary sinus is a curved, generally tubularstructure typically having a lesser radius of curvature (the inner sideof the curved tube) and a greater radius of curvature (the outer side ofthe curved tube). The coronary sinus is generally wider at its ostiumand tapers inwardly away from the ostium towards the distal portions ofthe coronary sinus. The ostium of the coronary sinus is located at thejuncture of the right atrium and the right ventricle.

To pace the left atrium, a pacing lead can be positioned so that anelectrode contacts the wall of the coronary sinus closest to the leftatrium. Because the coronary sinus is in electrical contact with theleft atrium, by pacing the coronary sinus at this position, one can alsopace the left atrium. The pacing lead generally is advanced to theostium of the coronary sinus through the right atrium portion of theright heart. For effective pacing, electrodes on the pacing lead shouldbe in constant electrical conductive contact with the wall of thecoronary sinus, preferably the left atrial side of the coronary sinus.Conductivity is preferably sufficient so as to enable a pacing voltageof 3 volts or less.

To accomplish constant wall contact, different pacing leadconfigurations have been used to assist in the placement and retentionof the pacing lead in the desired position. These prior leads, however,all have certain drawbacks making them not entirely satisfactory. Forexample, leads have been used in which a body of the lead is pre-formedto have a sinusoidal or helical configuration enabling the lead toexpand into contact with the walls of the coronary sinus and retain thelead. Examples of such pre-formed coronary sinus leads are disclosed inU.S. Pat. No. 5,423,865 to Bowald et al. and U.S. Pat. No. 5,476,498 toAyers. Such shapes, however, if not carefully sized to the diameter ofthe coronary sinus do not necessarily bias the electrodes against thewall of the coronary sinus with sufficient force to ensure goodelectrical connectivity resulting in instability and high pacingthresholds. Moreover, with helical shape leads, the electrodes may bedifficult to properly position relative to the coronary sinus wall foroptimal contact and thresholds.

Referring to FIGS. 1 a-1 f, specific examples of pre-formed coronarysinus leads are depicted and described in U.S. Pat. No. 6,321,123 toMorris et al, which is incorporated herein by reference. Pacing leads 20according to Morris et al. generally include a proximal lead portion 21with a first curved portion 22, a second curved portion 24, a tipelectrode 26, and additional electrodes 28 longitudinally disposedrelative to proximal lead portion 21. A sheath and straightening styletor guidewire is used to insert the lead 20 tip first into a coronarysinus. Once the sheath and lead 20 are within the coronary sinus, thesheath is removed and the lead 20 resiliently flexes toward itspre-formed shape. The pre-formed “J” in the lead 20 can cause the tip 26to be pressed up against the wall of the coronary sinus as depicted inFIGS. 1 c and 1 d, but only if the width of the pre-formed pacing lead20 is greater than that of the coronary sinus. The tip and otherelectodes, however, may not be in an optimal geometric relationship withthe wall of the coronary sinus, since the lead cannot fully assume itspreformed shape. Moreover, the biasing force exerted by the lead hasboth a laterally directed component, annotated as F₁ in the figures, anda longitudinally directed component, annotated as F₂ in the figures. Thelongitudinally directed component of the biasing force tends to urge thelead longitudinally backward in the coronary sinus toward the ostium,thereby reducing lead stability.

When the coronary sinus is wider than the pacing lead 20, the lead mayassume a loop shape longitudinally disposed relative to proximal leadportion 21 as depicted in FIGS. 1 b, 1 e and 1 f. In this case, thelongitudinally directed component of the biasing force F₂ is generallyrelatively less due to the contact of the lead with the coronary sinuswall laterally opposite the tip 26, but the resilience of the lead mayprovide little or no laterally directed biasing force F₁ for goodelectrical conductivity, and in some cases the tip electrode can losecontact with the wall of the coronary sinus altogether. This can lead tohigher voltage requirements, greater instability and higher pacing andsensing thresholds.

Referring to FIG. 2, there are also other pacing leads 30 that can beused to pace the left atrium through the coronary sinus, such as theMedtronic Attain® Bipolar OTW Lead Model No. 4194 and leads as disclosedin U.S. Pat. No. 5,683,445 to Swoyer, both of which are incorporatedherein by reference. The pacing lead 30 generally includes a firstcurved portion 32, a second curved portion 34, and a tip electrode 36.As depicted in FIG. 2, the angle 31 at the first curve 32 is greaterthan ninety degrees. Again, a sheath and stylet are used to insert thelead 30 tip first into a coronary sinus. Once the sheath and lead 30 arewithin the coronary sinus, the sheath and stylet are removed and thelead 30 takes its pre-formed shape, enabling the tip electrode 36 tocontact the walls of the coronary sinus if the diameter of the coronarysinus is less than the width of the pre-formed shape of the lead. Againhowever, using these leads to pace the coronary sinus presents the sameproblems inherent with the leads according to Morris et al. as describedabove.

The present inventor has recognized that prior art leads and fixationmethods provide a success rate of 60% or less when used to pace the leftatrium via the coronary sinus. Hence, there is still a need for a leadand fixation method assuring stable pacing of the left atrium throughthe coronary sinus. Because the general problems discussed above havenot been addressed by conventional pacing leads, there is a current needfor pacing leads addressing the problems and deficiencies inherent withconventional designs.

SUMMARY OF THE INVENTION

The pacing lead of the various embodiments of the present inventionsubstantially addresses the aforementioned problems of conventionaldesigns by providing lead shapes and methods of pacing lead deploymentthat assure that the electrodes of the lead are firmly in electricalconductive contact with the wall of the coronary sinus so as to enablepacing voltages of 3 volts or less. In an embodiment, the improvedpacing is accomplished because as the lead is advanced into the coronarysinus, a resilient fixation element preformed in a prolapsed position soas to be laterally adjacent the lead body, is laterally compressed bythe walls of the coronary sinus as it is advanced into the coronarysinus. The resilience of the fixation element biases the lead body andportions of the fixation element against the wall of the coronary sinus,thereby improving electrical conductivity between the coronary sinuswall and electrodes disposed on the lead body or on the biased portionsof the fixation element. In addition, in embodiments with a tipelectrode, the prolapsed fixation element insures that the tip electrodeis fixed relative to the coronary sinus closest to the left atrium, thusresulting in lower pacing voltages and thresholds and higher pacingstability.

In another embodiment, the lead has a pacing portion and a resilientfixation element extending distally from the pacing portion. The pacingportion includes a proximal electrode and a distal electrode. Thefixation element is preformed so as to be doubled-back or prolapsedalong the pacing portion, forming a loop structure. The width dimensionof the preformed loop structure is predetermined so as to be larger thanthe diameter of the coronary sinus. When the loop structure is advancedinto the coronary sinus, the loop is compressed in the width directionso that the electrodes of the pacing portion are biased against the wallof the coronary sinus by the resilience of the fixation element, therebyimproving electrode conductive contact with the wall of the coronarysinus and resulting in improved stability and lower pacing and sensingthresholds. The electrodes of the pacing portion are biased against thewall of the coronary sinus (lesser curvature) where the left atrium isin proximity to the coronary sinus because the pacing lead proximal tothe fixation element conforms naturally to the lesser curvature of thecoronary sinus.

According to an embodiment, a pacing lead for implantation in a coronarysinus having an opening and a wall defining an interior and presenting adiameter dimension, includes an elongated lead body having a pacingportion with at least one electrode and a resilient fixation element.The fixation element extends from the pacing portion and defines a loopstructure laterally adjacent the pacing portion. The loop structurepresents a predetermined width dimension greater than the diameterdimension of the coronary sinus, wherein when the loop structure isadvanced into the opening of the coronary sinus, the loop structure islaterally compressed by the wall of the coronary sinus and the at leastone electrode is biased against the wall of the coronary sinus.

According to an embodiment of a method according to the invention, apacing lead is provided having a lead body with a resilient fixationelement extending from a distal end thereof. The resilient fixationelement is preformed in a prolapsed configuration so as to form a looplaterally adjacent the lead body. According to the method, the prolapsedform of the fixation element is deployed with the lead positionedoutside of the ostium of the coronary sinus. The fixation element isthen advanced into the coronary sinus so that the loop structure of thefixation element is laterally compressed by the wall of the coronarysinus, thereby biasing electrodes on the lead body or fixation elementagainst the wall of the coronary sinus.

A feature and advantage of an embodiment of the invention is that theleft atrium can be paced by directing the tip electrode towards the leftatrium side of the coronary sinus.

A feature and advantage of an embodiment of the invention is thatassuring constant contact between the lead electrodes and the walls ofthe coronary sinus can increase the stability of the fixation andpacing.

A feature and advantage of an embodiment of the invention is that thedesign of the pacing lead enables use on various sized coronary sinuseswithout sacrificing stability or pacing/sensing thresholds.

A feature and advantage of an embodiment of the invention is a method ofpacing lead deployment assuring constant contact between the leadelectrodes and the walls of the coronary sinus.

A feature and advantage of an embodiment of the invention is that theleft atrium can be paced by biasing one or more lead electrode againstthe wall of the coronary sinus using a resilient fixation element of thelead.

A feature and advantage of an embodiment of the invention is that theresilient fixation element of the lead may or may not contain electrodesfor sensing and pacing the left atrium via the coronary sinus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a fragmentary elevational view of a prior art coronary sinuspacing lead;

FIG. 1 b-1 f are fragmentary cross-sectional views of a coronary sinusdepicting prior art coronary sinus pacing leads being inserted into thecoronary sinus;

FIG. 2 is a fragmentary elevational view of a prior art left-ventriclepacing lead;

FIG. 3 is a fragmentary elevational view of a coronary sinus pacing leadaccording to an embodiment of the present invention;

FIG. 4 is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention prior to being inserted into the coronary sinus;

FIG. 5 is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention being inserted into the coronary sinus;

FIG. 6 is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention inserted into the coronary sinus;

FIG. 7 is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention inserted into the coronary sinus;

FIG. 8 is a fragmentary elevation view of a coronary sinus pacing leadaccording to an embodiment of the present invention;

FIG. 9 is a fragmentary elevation view of a coronary sinus pacing leadaccording to an embodiment of the present invention;

FIG. 10 is a fragmentary elevation view of a coronary sinus pacing leadaccording to an embodiment of the present invention;

FIG. 11 is a fragmentary elevation view of a coronary sinus pacing leadaccording to an embodiment of the present invention;

FIG. 12 is a fragmentary cross-sectional view of the coronary sinus leadof FIG. 8, taken along a longitudinal axis of the lead;

FIG. 13 is a fragmentary cross-sectional view of the coronary sinus leadof FIG. 9, taken along a longitudinal axis of the lead;

FIG. 14 is a fragmentary cross-sectional view of the coronary sinus leadof FIG. 10, taken along a longitudinal axis of the lead;

FIG. 15 is a fragmentary elevation view of the coronary sinus pacinglead according to an embodiment of the present invention;

FIG. 16 is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention in a straightened orientation in a sheath prior tobeing inserted into the coronary sinus;

FIG. 16 a is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention in an alternative prolapsed orientation in a sheathprior to being inserted into the coronary sinus;

FIG. 17 is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention being inserted into the coronary sinus; and

FIG. 18 is a fragmentary cross-sectional view of a coronary sinusdepicting a coronary sinus pacing lead according to an embodiment of thepresent invention inserted into the coronary sinus.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 3, a pacing lead 40 according to the variousembodiments of the present invention generally includes a proximal leadportion 42 presenting a lead axis 42 a terminating in the fixationelement 43 of the pacing lead at a first or proximal curve 44 having afirst angle 46, a second or distal curve 50 having a second angle 52,and a tip 57 with a tip electrode 56 and presenting a longitudinal leadtip axis 57 a. Lead 40 is preformed in a prolapsed configuration, withfixation element 43 doubled back so as to be laterally adjacent proximallead portion 42 forming a loop structure 57 a. A first section 48 isgenerally defined between the first and second curves 44, 50 and asecond section 54 is generally defined between the second curve 50 andthe tip electrode 56. The pacing lead 40 may also include additionalcurves and sections disposed between the first and second curves. Thepacing lead 40 can also include additional curves and sections disposedbetween the tip of the pacing lead and the second curve. Fixationelement 43 can also be configured in a continuous curve with a varietyof radius arcs. Pacing leads are generally known in the art and aredisclosed in U.S. Pat. No. 6,321,123 to Morris et al. and U.S. Pat. No.5,683,445 to Swoyer, both of which are incorporated herein by referencein their entirety.

The pacing lead 40 can also include one or more electrodes 58 disposedat any desired point on the proximal lead portion 42 or fixation element43. The pacing lead 40 can further include a stylet 60 slidably disposedin the lead to initially straighten the preformed shape and which thenmay be withdrawn to the start of the fixation element to enable thepreformed shape to develop and to selectively maintain the stiffness ofthe pacing lead 40 as the lead 40 is advanced into and positioned withinthe coronary sinus. It will also be appreciated that the shape of tipelectrode 56 may be modified as desired, for example by maximizingcontact surface area, to enable better contact with the wall of thecoronary sinus and resultantly better performance.

The respective lengths of the first and second sections 48, 54 and thefirst and second angles 46, 52 between the first and second sections 48,54 of the pacing lead 40 can be selected so that the tip electrode 56will be in constant contact with the left atrial wall of the coronarysinus, i.e., to maximize contact between the tip electrode 46 and theleft atrial wall of the coronary sinus. The overall length L and width Wof the first and second sections 48, 54 can also be selected so that thetip electrode 56 will be in constant contact with the left atrial wallof the coronary sinus. The dimensions of the pacing lead according toexemplary embodiments of the present invention can be seen in Table I.Generally, the width of the pacing lead is preferably from about 10% to200% greater than the diameter of the coronary sinus, more preferablyfrom about 25% to about 75% greater than the diameter of the coronarysinus, and most preferably about 50% greater than the diameter of thecoronary sinus for stability and good electrical contact. TABLE I Pacinglead dimensions according to various exemplary embodiments. First SecondExemplary Exemplary Range Embodiment Embodiment Lead Width (French) 2 Fto 9 F  5 F ± 1 F  5 F ± 1 F Width—W (mm) 2.0 to 20.0  7.0 ± 5.0  7.0 ±5.0 Length—L (mm) 5.0 to 60.0 30.0 ± 5.0 30.0 ± 5.0 First Section (mm)2.0 to 30.0   10 ± 5.0 20.0 ± [10.0 cm] Second Section (mm) 2.0 to 30.0  10 ± 5.0 20.0 ± [10.0 cm] First angle* (degrees)  90-165   45 ± 5   45± 5 Second angle* (degrees) 105-165  120 ± 30  120 ± 30*Pre-formed angle prior to insertion into the coronary sinus.

While dimensions of the pacing lead 40 according to exemplaryembodiments of the present invention are listed in Table I, one skilledin the art will recognize that changes may be made in form and detail ofthe dimensions without departing from the spirit and the scope of theinvention. Therefore, the exemplary embodiments listed in Table I shouldbe considered in all respects as illustrative and not restrictive.

Referring to FIGS. 4-6, implanting the pacing lead 40 into the coronarysinus can be accomplished by first inserting a stylet 60 into the pacinglead 40 and then advancing the pacing lead 40 with stylet 60 towards theostium of the coronary sinus. Introducers for accessing the coronarysinus of the heart can be seen in U.S. Patent Application PublicationNos. 2003/0208141A1, 2004/0019359A1, and 2003/0208220A1, each to Worleyet al., which are incorporated herein by reference. The implantation canbe done using a guide wire supported guiding catheter 62 having a sheath64 and guide support wire 66. A guide wire supported guiding catheter 62is disclosed, for example, in U.S. Pat. No. 6,714,823, which isincorporated herein by reference. Alternatively, where the coronarysinus is of a smaller diameter, or where it is desired to pace thesmaller diameter distal portion of the coronary sinus, pacing lead 40may be inserted tip first using a sheath and stylet.

To implant the pacing lead 40 using a guiding catheter 62, one end ofthe guide wire 66 is first inserted deep into the coronary sinus. Theother end of the guide wire 66 is operably coupled to the sheath 64 ofthe guiding catheter 62. The guide wire 66 can then maintain thepositioning of the sheath 64 proximate the ostium of the coronary sinus.

Once the sheath 64 is held into place proximate the ostium of thecoronary sinus, the stylet 60 of the pacing lead 40 is withdrawn out ofthe pacing lead 40 to a position proximate the first or proximal bend 44of the pacing lead 40. The pacing lead 40 can then be advanced out ofthe sheath 64 to deploy the preformed loop of fixation element 43 whilemaintaining the stylet 60 at its position proximate the first bend 44 ofthe lead 40.

After the pacing lead 40 has been deployed out of the sheath 64 so thatthe lead 40 takes its pre-formed loop shape, the stylet 60 is kept atthe first bend 44 of the pacing lead 40 while the lead 40 and stylet 60are advanced into the coronary sinus, proximal bend 44 first. As statedabove in Table I, in a first embodiment of the present invention, thefirst angle 46 between the first and second sections 48, 54, in itspre-formed configuration, is approximately 120 degrees.

As the pacing lead 40 is inserted into the ostium of the coronary sinus,the first angle 46 will compress or decrease until the tip electrode 56comes into contact with the wall of the coronary sinus. Once thishappens, the second angle 52 between the first and second sections 48,54 will increase, e.g., to approximately one hundred and fifty degrees,due to compressive forces placed on the tip 56 as the pacing lead 40progresses into the narrowing structure of the coronary sinus. In otherwords, in this wedged position, the walls of the coronary sinus flattenthe distal curve 50 as the lead 40 is advanced into the tapering tubularstructure of the coronary sinus. The tapering shape of the coronarysinus maximizes the contact between the tip electrode 56 and left atriumside of the coronary sinus.

By compressing the proximal and distal curves 44, 50, the lead 40 foldsover and the tip electrode 56 is pressed against the left atrial side ofthe coronary sinus, thus improving the contact between the tip electrode56 and the wall of the coronary sinus. Contact between the tip electrode26 and the coronary sinus is maintained as the pacing lead 40 expands toassume its natural, expanded state. The contact results in lower pacingvoltages and thresholds and higher pacing stability. The contact alsoinhibits any movement of the pacing lead 40 due to the heart beating andbreathing of the patient once it is in its place within the coronarysinus. In this position, the coil or ring electrode 58 also has improvedcontact with the wall of the coronary sinus, as depicted in FIG. 7.

In an alternative embodiments depicted in FIGS. 8-14, lead 40 generallyincludes lead body 67 with pacing portion 68 and with fixation element70 extending distally from lead body 67. Lead body 67 generally includesinner body 72 defining central lumen 74, inner conductor 76 which iselectrically coupled with distal electrode 78, inner insulative sheath80, outer conductor 82 which is electrically coupled with proximalelectrode 84, and outer insulative sheath 86. Electrodes 78, 84, may bestructured as rings 88 encircling lead 40, may be dorsal protuberances90, or may be any other suitable structure enabling electrical couplingwith the wall of the coronary sinus. Conductors 76, 82, may be coiledwire as commonly used in the art, or may be any other suitable generallyflexible conductive structure. Inner body 72 and insulative sheathes 80,86, may be formed from silicone, polyurethane, or other resilientbiocompatible material.

As depicted in FIGS. 8-14, fixation element 70 may be integral withinner body 72 of lead body 67. According to the invention, fixationelement 70 is preformed with a proximal portion 92 and distal portion94, which together define a loop structure 96 laterally adjacent leadbody 67. Loop structure 96 presents a width dimension, annotated “W” inthe figures. As depicted, either or both of proximal portion 92 anddistal portion 94 may be generally arcuate in shape or may be generallystraight. In embodiments of the invention, a straight portion 97 may beinterposed between proximal portion 92 and distal curved 94 as depictedin FIG. 11. Additionally, as depicted in FIG. 15, a short opposite bend99 may be included between pacing portion 68 and proximal portion 92 toimprove electrode contact with the coronary sinus wall when lead 40 isimplanted.

In embodiments where proximal and distal portions 92, 94, are arcuate asdepicted for example in FIG. 12, proximal portion 92 desirably subtendsan angle a of at least about 120 degrees and preferably about 180degrees, and distal portion 94 subtends an angle of between about 40 andabout 90 degrees. In embodiments where proximal and distal portions 92,94, are generally straight as depicted for example in FIG. 11, proximalportion 92 preferably forms an angle γ with pacing portion 68 of lessthan 90 degrees. Distal portion 94 preferably forms an angle δ withrespect to proximal portion 92 of between about 90 and about 150degrees.

Central lumen 74 may terminate in pacing portion 68 as depicted in FIGS.10 and 14, may extend into fixation element 70, terminating in anaperture 98 leading to the outside surface 100 of the lead as depictedin FIGS. 8 and 12, or may extend through to tip 102 as depicted in FIGS.9 and 13. It will be readily appreciated that in the embodiment of FIGS.8 and 12, aperture 98 may be positioned and dimensions so that whenfixation element 70 is straightened, aperture 98 is partially or fullyclosed. In some embodiments, lead 40 is packaged with fixation element70 held straight with a straightening member (not depicted). Thestraightening member is removed prior to or during insertion of lead 40to enable fixation element 70 to assume its preformed shape.

The lateral biasing force exerted by the resilience of the fixationelement is a function of the material properties, the cross-sectionaldimension of the fixation element, and the amount of lateral deflection,annotated in the figures as ΔD_(fx) of the fixation element. The amountof lateral deflection of the fixation element will vary depending on thediameter of the coronary sinus, and will generally be between about 0.5centimeters and 12 centimeters, most typically from about 1.5centimeters to about 6 centimeters. It will be appreciated that themagnitude of lateral biasing force may be predetermined by adjusting thematerial properties and dimensions of the fixation element using knownprinciples of engineering. Generally, it is desirable if the fixationelement provides between about 1 gram to about 30 grams of biasing forceand more desirably between about 3 grams to about 10 grams when fixed inthe coronary sinus.

Again, to implant the pacing lead 40 using a guiding catheter 62, oneend of the guide wire 66 is first inserted deep into the coronary sinusas depicted in FIGS. 16 and 16 a. The other end of the guide wire 66 isoperably coupled to the sheath 64 of the guiding catheter 62. The guidewire 66 can then maintain the positioning of the sheath 64 proximate theostium of the coronary sinus. Stylet 60 is inserted in central lumen 74of lead 40 and the lead is advanced into sheath 64 in a straightenedorientation as depicted in FIG. 16 or alternatively in a prolapsedorientation as depicted in FIG. 16 a. Alternatively, in the embodimentof FIG. 12, lead 40 may be advanced into sheath 64 with guide wire 66extending through aperture 98 and central lumen 74. In this embodiment,central lumen 74 also accommodates stylet 60 to enable lead 40 to beadvanced along the guide wire.

Once the sheath 64 is held into place proximate the ostium of thecoronary sinus, the stylet 60 of the pacing lead 40 is withdrawn to aposition proximate the proximal portion 62 of pacing lead 40. The pacinglead 40 is then deployed out of the sheath 64. After the pacing lead 40has been advanced out of the sheath 64 and any straightening member hasbeen removed so that fixation element 70 takes its pre-formed loop shapewith fixation element 70 in a prolapsed configuration laterally adjacentlead body 67, the lead 40 and stylet 60 are advanced into the coronarysinus, proximal portion 92 first as depicted in FIG. 17. As the pacinglead 40 is inserted into the ostium of the coronary sinus, the loopstructure 96, the uncompressed width W of which is greater than thediameter D of the coronary sinus, is compressed laterally in thedirection of the arrow by the walls of the coronary sinus. Oncecompletely in place with fixation element 70 deflected inwardly by anamount ΔD_(fx) as depicted in FIG. 18, the deflection of resilientfixation element 70 biases lead body 67 and electrodes 78, 84, againstthe wall of the coronary sinus. The improved electrode conductivecontact resulting from the biasing force applied by fixation element 70enables lower pacing voltages and thresholds and improves leadstability. The contact also inhibits any movement of the pacing lead 40due to the heart beating and breathing of the patient once it is in itsplace within the coronary sinus.

It will be readily appreciated that, in addition to the embodimentsdisclosed above, a pacing lead according to the invention may take avariety of alternative forms, each including a fixation elementprolapsed so as to form a loop structure laterally adjacent a bodyportion of the lead. For the purposes of the present invention, the termloop structure includes any lead wherein the lead tip 57 a, 102, isdoubled back along the lead body and a longitudinal axis extending fromthe lead tip 57 a, 102, parallels or intersects a longitudinal axis ofthe lead body when the tip and lead body axes are projected onto acommon plane parallel to and including the lead body axis. For instance,the fixation element forming a loop structure may include a plurality ofmore or less straight segments angled with respect to each other, or aplurality of curved segments of various radii, a single segment with amore or less continuous curve, or a plurality of straight and curvedsegments joined together. The fixation element and lead body may be madewith any material having suitable engineering and biocompatibilityproperties. The lead electrodes may take any suitable form includingwithout limitation, coils or rings, and “buttons” or protuberances, andmay be positioned on the lead body or the fixation element or anycombination thereof. It may be relatively more desirable, however, tolocate the electrodes proximal to any relatively sharp angles or bendsin the lead so as to avoid fractures in the conductors leading to theelectrodes.

While insertion of the pacing lead into the coronary sinus has beendepicted and described as being done by deploying the lead outside theostium of the coronary sinus so that lead takes its pre-formed shapebefore it is advanced into the coronary sinus, in other embodiments,such as where the coronary sinus has a smaller diameter, the pacing leadcan be introduced tip-first in the coronary sinus in the conventionalfashion.

Although the present invention has been described with reference toparticular embodiments, one skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand the scope of the invention. Therefore, the illustrated embodimentsshould be considered in all respects as illustrative and notrestrictive.

1. A pacing lead for implantation in a coronary sinus having an openingand a wall defining an interior and presenting a diameter dimension, thepacing lead comprising an elongated lead body with a resilient fixationelement extending therefrom and defining a loop structure laterallyadjacent the lead body, the pacing lead further including at least oneelectrode on either the lead body or the fixation element, the loopstructure presenting a predetermined width dimension greater than thediameter dimension of the coronary sinus, wherein when the loopstructure is inserted into the opening of the coronary sinus, the loopstructure is laterally compressed by the wall of the coronary sinus andthe at least one electrode is biased against the wall of the coronarysinus.
 2. The lead of claim 1, wherein the lead includes a pair ofelectrodes.
 3. The lead of claim 2, wherein the pair of electrodes isdisposed on the lead body.
 4. The lead of claim 1, wherein the loopstructure includes a generally arcuate proximal portion and a generallyarcuate distal portion.
 5. The lead of claim 4, wherein the generallyarcuate proximal portion subtends an angle of at least about 120degrees.
 6. The lead of claim 5, wherein the generally arcuate proximalportion subtends an angle of about 180 degrees.
 7. The lead of claim 4,wherein the generally arcuate distal portion subtends an angle of atleast about 40 degrees.
 8. The lead of claim 7, wherein the generallyarcuate distal portion subtends an angle of about 90 degrees.
 9. Thelead of claim 4, wherein the loop structure includes a generallystraight portion between the generally arcuate proximal portion and thegenerally arcuate distal portion.
 10. The lead of claim 1, wherein theloop structure includes a generally straight proximal portion definingan angle with the pacing portion of less than 90 degrees.
 11. The leadof claim 10, wherein the loop structure includes a generally straightdistal portion defining an angle with the generally straight proximalportion of between about 90 and about 150 degrees.
 12. The lead of claim11, wherein the loop structure includes a generally straight portionbetween the generally straight proximal portion and the generallystraight distal portion.
 13. The lead of claim 1, wherein the leaddefines a central lumen.
 14. The lead of claim 13, wherein the centrallumen extends through the lead body and the resilient fixation element.15. The lead of claim 13, wherein the lead defines an aperture extendingfrom the central lumen to an exterior surface of the lead.
 16. The leadof claim 1, further comprising a catheter and a guidewire operablycoupled to the catheter for guiding the lead towards the opening of thecoronary sinus.
 17. The lead of claim 16, wherein the lead defines anaperture extending from the central lumen to an exterior surface of thelead, the guidewire extending through the central lumen and aperture ofthe lead.
 18. The lead of claim 1, wherein the lead comprises a leadwidth, the lead width being between 4 and 6 French.
 19. The lead ofclaim 1, wherein the predetermined width dimension is between about 10%and about 200% of the diameter dimension of the coronary sinus.
 20. Thelead of claim 1, wherein the predetermined width dimension is betweenabout 25% and about 75% of the diameter dimension of the coronary sinus.21. A method of inserting a pacing lead having a preformed shape into acoronary sinus to pace a left atrium, the coronary sinus having anopening and a wall defining an interior and presenting a diameterdimension, the method comprising: providing a pacing lead comprising anelongated lead body having a pacing portion with at least one electrodeand a resilient fixation element, the fixation element extending fromthe pacing portion and defining a preformed loop structure laterallyadjacent the pacing portion, the loop structure presenting apredetermined width dimension greater than the diameter dimension of thecoronary sinus; advancing the loop structure into the interior of thecoronary sinus, such that the loop structure is operably laterallycompressed by the coronary sinus wall thereby biasing the pacing portionand at least one electrode against the wall of the coronary sinusproximate the left atrium.
 22. The method of claim 21, furthercomprising: providing a pair of electrodes disposed on the pacingportion of the lead; advancing the loop structure into the interior ofthe coronary sinus, such that both electrodes are biased against thewall of the coronary sinus.
 23. The method of claim 21, furthercomprising: providing a guide catheter having a guide wire operablycoupled thereto for guiding the pacing lead towards the coronary sinusopening; anchoring the guide wire into at least a portion of thecoronary sinus; inserting the pacing lead into the guide catheter withthe fixation element held in a straightened position; advancing theguide catheter and pacing lead to a position proximate the opening ofthe coronary sinus; and advancing the pacing lead out of the sheathtowards the opening of the coronary sinus such that the fixation elementdefines the preformed loop structure prior to advancing the loopstructure into the interior of the coronary sinus.
 24. A pacing leadconfigured for implantation in a coronary sinus having an opening and awall defining an interior, the pacing lead comprising an elongated leadbody with at least one electrode and presenting a lead body axis, thepacing lead further including a resilient fixation element extendingfrom the lead body and having a tip presenting a tip axis, the resilientfixation element defining a loop structure laterally adjacent the pacingportion, the loop structure presenting a predetermined width dimensiongreater than the diameter dimension of the coronary sinus, wherein whenthe loop structure is inserted into the opening of the coronary sinus,the loop structure is laterally compressed by the wall of the coronarysinus and the at least one electrode is biased against the wall of thecoronary sinus.
 25. The lead of claim 24, wherein the lead includes apair of electrodes.
 26. The lead of claim 25, wherein the pair ofelectrodes is disposed on the lead body.
 27. The lead of claim 24,wherein the lead defines a central lumen.
 28. The lead of claim 27,wherein the central lumen extends through the lead body and theresilient fixation element.
 29. The lead of claim 27, wherein the leaddefines an aperture extending from the central lumen to an exteriorsurface of the lead.
 30. The lead of claim 24, further comprising acatheter and a guidewire operably coupled to the catheter for guidingthe lead towards the opening of the coronary sinus.
 31. The lead ofclaim 30, wherein the lead defines an aperture extending from thecentral lumen to an exterior surface of the lead, the guidewireextending through the central lumen and aperture of the lead.
 32. Thelead of claim 24, wherein the predetermined width dimension is betweenabout 10% and about 200% of the diameter dimension of the coronarysinus.
 33. The lead of claim 24, wherein the predetermined widthdimension is between about 25% and about 75% of the diameter dimensionof the coronary sinus.
 34. A method of inserting a pacing lead having apreformed shape into a coronary sinus, the coronary sinus having anopening and a wall defining an interior and presenting a diameterdimension, the method comprising: providing a pacing lead comprising anelongated lead body and a resilient fixation element with at least oneelectrode on either the lead body or the fixation element, the fixationelement extending from the lead body and defining a preformed loopstructure laterally adjacent the lead body, the loop structurepresenting a predetermined width dimension greater than the diameterdimension of the coronary sinus; deploying the loop structure outsidethe opening of the coronary sinus; and advancing the loop structure intothe interior of the coronary sinus, such that the loop structure isoperably laterally compressed by the coronary sinus wall thereby biasingthe at least one electrode against the wall of the coronary sinus.